Such a keyboard is known from EP 1876620 A1. Said keyboard has a keypad having a plurality of plate-shaped, rigid keys which are guided displaceably in recesses of a cover plate. Each of said keys is connected to an associated actuator of a flexible switching membrane, with the switching membrane having for each key an electrically conductive layer which is respectively associated with a pair of switching contacts on a conductor board. The individual keys are adhered to the associated actuator.
Upon depression of a key the latter depresses the associated actuator whose electrically conductive contact area then touches the contact pair on the conductor board and thus closes an electrical contact. Upon release of the key the actuator and the switching membrane spring back to their starting positions and then open the associated electrical contact. The actuators and the switching membrane are made of rubber-elastic material and are hence flexible in all spatial directions, the consequence being that the plate-shaped, almost entirely rigid keys also carry out tilting or wobbling motions when they are subjected to a force not exactly in the center. Also, the keys can be displaced in a plane (X, Y) that is parallel to their surfaces. In so doing, they can get wedged and be jammed in the cover plate. Also, it is not ensured that the desired electrical contact is closed, since a “lopsided” depression of the key can convey to the user the impression that the key is completely depressed while in fact the associated actuator is insufficiently depressed and deformed to electrically connect the associated contact pair on the conductor board.
U.S. Pat. No. 4,520,248 A shows a keyboard having a plurality of keys respectively separated from each other by a gap and fastened to an elastic foam layer. On the side of the foam layer opposing the keys is arranged a switching membrane with electrically conductive regions which are held by spacers relative to a conductor board. Through the foam layer, the keys can also perform tilting or wobbling motions upon depression, which has the above-described disadvantages.
DE 10 2004 021 542 A1 shows a keyboard having rubber-elastic actuators which are respectively covered by a rigid cap, with the caps being guided displaceably in a cover layer.